Brachytherapy strands are cancer therapy devices in which radioactive brachytherapy seeds are provided in an elongate carrier. One such device marketed by the assignee of the present invention is RAPID Strand®, available from its Arlington Heights, Ill. facility. RAPID Strand® is manufactured using a Polyglactin braided carrier. Polyglactin is a mixture of polyglocolide and poly l-lactide and is commonly used as a biologically absorbable material. FIG. 1 depicts a RAPID Strand® product 10 as presently manufactured and sold by GE Healthcare of North Arlington Heights, Ill. The braided carrier 12, clearly seen in FIG. 1, contains radioactive seeds and non-radioactive spacers. The locations of the seeds and spacers are noted by the reference numbers 14 and 16, respectively. The seeds are the cancer therapy components. The spacers are used for optimum seed separation and long axis rigidity of the assembled RAPID Strand®. The seeds and spacers are inserted into the braided carrier, and then the assembled unit is heated in an oven. The oven cycle causes the braided carrier, and seeds and spacers contained within it, to gain enormous strength long axis. This is accomplished by a thermo-induced change in the structure of the Polyglactin material. This heat stiffening process takes considerable time and energy to perform, but is required for finished device assembly functionality.
During implant preparation it is common to cut the standard RAPID Strand® segments into smaller segments for optimum clinical value to the patient. One such method is described in U.S. Pat. No. 5,460,592 assigned to the assignee of the present invention and the contents of which are hereby incorporated by reference as if fully stated herein. When cutting the segments it is not uncommon for the inner components to become somewhat separate from the outer braid. Heating the end, after cutting the segment, can help in retaining the components in the braided carrier material. It should be noted that the seed components themselves are made of titanium and have no physical connection to the braided carrier or the spacers. The seeds are contained within the heat-stiffened suture and between the spacers. Long axis rigidity is accomplished by having components (seeds and spacers) stacked end to end within a very tight braided material.
There is therefore a need for an alternative method for imparting long-axis stiffness, and end spacer retention when cut, to a brachytherapy strand. There is also a need for an elongate brachytherapy strand having regions of longitudinal stiffness adjacent regions of considerably reduced longitudinal stiffness to facilitate deflection of the strand when used for applications in which it is desired for the strand to more closely conform to deflectable tissue, such as lung tissue during the process of inhalation and exhalation.